1. Field of Invention
The present invention relates to a fuel cell, and more particularly to a method for fabricating a bi-polar plate of a fuel cell and the bi-polar plate thereof.
2. Related Art
The fuel cell, characterized in having high efficiency, quick reaction, silent operation, and low pollution, is widely applied in fields such as electricity, industry, transportation, space, and military. The fuel cell is a power generation device capable of continuously converting chemical energy into electric energy directly. When the fuel cell is working, a fuel gas (for example, H2) and a combustion supporting agent (for example, O2) are transferred to an anode and a cathode of the fuel cell respectively, and the chemical energy is converted into electric energy through oxidation and reduction reactions.
The structure of a conventional fuel cell is generally formed of an anode plate, a cathode plate, and a solid electrolyte membrane sandwiched therebetween, which is also called a single cell. However, in practice, a plurality of single cells is connected in series to obtain a large output voltage. The adjacent fuel cells share one electrode plate, so that the electrode plate serves as both an anode and a cathode of the two adjacent fuel cells, and is thus referred to as a bi-polar plate.
The bi-polar plate is mainly made of a material having high electrical conductivity such as graphite, composite carbon, and metal. In order to satisfy the demand for high power density, light weight, and flexibility of the fuel cell in the market, the bi-polar plate needs to be designed lighter and thinner. However, if the graphite plate or composite carbon plate is made very thin, problems including undesirable air-tightness and insufficient structural strength of the bi-polar plate may occur, or fractures during processing or use may be easily caused due to material characteristics of the graphite such as low hardness and poor ductility.
The metallic material is easily processed and suitable for mass production, and also has excellent electrical conductivity and thermal conductivity, so that a thin and light bi-polar plate can be obtained with such the material. However, in the working process of the fuel cell, due to the reaction of the fuel or oxidant, the surface of the metal bi-polar plate may be easily oxidized and corroded to cause deterioration of the performance of the fuel cell and shortening of its service life. If corrosion-resistant noble metal, such as Au or Pt, is used to fabricate the bi-polar plate, or a protection layer made of noble metal is plated on the surface of the metal bi-polar plate, the manufacturing cost becomes rather high.
Taking a bi-polar plate made of a corrosion-resistant metallic material such as stainless steel, Al, or Ti for example, a dense oxidation layer formed of oxides can be provided on a surface of the bi-polar plate to avoid corrosion on the surface of the bi-polar plate caused by the electrolyte. However, the oxidation layer may also raise the contact resistance of the surface, so that the capability of the bi-polar plate for conducting electrons is deteriorated, and a total output voltage of the fuel cell is reduced.